Due to the work pressure, air and environment pollution and many other factors, the incidence of human respiratory diseases remains high, while cough is a common and frequently-occurring disease of respiratory system and is a common chief complaint of respiratory outpatient. The cough itself is a defensive reflex activity generated when the respiratory system is stimulated, is a beneficial action, and sometimes is also found in healthy people. In general, mild and infrequent coughs can be relieved naturally without applying antitussive medicines. In addition, impact of the cough on human health is also dialectical and is also a pathological reaction; and long-term frequent or too intense cough not only may increase the suffering of patients, affect the rest and sleep and increase the physical exertion, but also may promote the development of diseases in severe cases to cause other complications.
According to different courses of the disease, the cough can be divided into acute cough, subacute cough and chronic cough. The course of acute cough is less than three weeks, that of subacute cough is three to eight weeks, and that of chronic cough is more than or equal to eight weeks. 1) The acute cough: at present, acute viral upper respiratory tract infection is generally considered as the most common cause, and others include rhinitis, sinusitis, acute bronchitis, acute exacerbation of chronic bronchitis, bronchial asthma and the like; the most common pathogens of upper respiratory tract infection are rhinovirus, coronavirus, respiratory syncytial virus, parainfluenza virus, adenovirus, enterovirus and the like, wherein rhinovirus is most common; the acute cough may also be associated with the acute exacerbation of asthma, bronchitis and other respiratory diseases; and clinically, many infectious diseases or some other diseases having the acute cough as a prodroma can often be seen. 2) The subacute cough: the most common causes are post-infectious cough (also known as post-cold cough), bacterial sinusitis, asthma and the like; a virus as the pathogen is commonly rhinovirus, accounting for about 30%-50%, followed by coronavirus and influenza virus, respectively accounting for 10%45% and 5%-15%; and in addition to respiratory viruses, mycoplasma pneumoniae, chlamydia pneumoniae and the like can also cause post-infectious cough. 3) The chronic cough: the chronic cough is usually used for defining a patient having cough as the only symptom or the main symptom, having the course of disease of more than eight weeks and having no apparent abnormality in chest X-ray examination in clinical practice, and is known as unexplained chronic cough, called chronic cough for short; the rate of chronic cough is up to 10%-38% in specialty clinic; questionnaires of European and American countries show that the incidence of chronic cough is also up to 9%-33%; and the common causes of chronic cough are eosinophilic bronchitis (EB), upper airway cough syndrome (UACS, formerly known as postnasal drip syndrome (PNDS)), gastroesophageal reflux cough (GERC), cough variant asthma (CVA) and the like.
A site investigation for the cough of 1087 college students of Guangzhou Institute of Respiratory Diseases in 2006 showed that the overall incidence of cough in groups was 10.9%, wherein the overall incidence of chronic cough was 3.3%. It can be speculated that the incidence of cough in community population may be higher, and the average course of disease of such patients was longer, some even up to decades of years. Some data showed that about 15% of adults and 10% of minors were affected by different degrees of cough all over the world every year. Therefore, the development of safe and effective antitussive medicines can create better social benefits and economic benefits while meeting a huge market demand.
According to different action mechanisms of medicines, the antitussive medicines can be divided into two categories as follows: the first category is centrally acting antitussive medicines; such medicines can directly and selectively inhibit the medullary respiratory center to generate an antitussive effect, such as morphine, codeine, etc.; and such medicines have better antitussive effect, but have obvious side effects, can lead to addiction and respiratory depression, and even induce hallucinations, delusions or other psychotic symptoms. The second category is peripherally acting antitussive medicines; such medicines block the afferent impulse of cough reflex by inhibiting the lung-vagal reflex, thereby playing an antitussive role, such as benproperine, benproperine phosphate, Moguisteine and the like; and most of such medicines are alkaloid medicines, and may cause nausea, palpitation, dizziness or other adverse reactions. Although various medicines can be used for relieving the cough clinically, many patients with chronic cough cannot get effective relief after treatment by using these medicines.
The traditional Chinese medicine is a crystallization of rich practical experience of Chinese people in the prevention and treatment of diseases for thousands of years. Doctors of traditional Chinese medicine may recognize some diseases unknown by doctors of western medicine. The traditional Chinese medicines may be used for treating some diseases refractory and incurable to western medicines. The traditional Chinese medicine has a long history and rich experience in the treatment of coughs, and is complementary with the western medicines used by the doctors of western medicine. Although there are a lot of traditional Chinese medicines and Chinese patent medicines for treating coughs in China at present, the effective components and the indications of these medicines are not clear. In addition, there is no good treatment medicine for patients with unexplained chronic cough and airway inflammation, so the primary task of pharmaceutical workers engaged in the field of respiratory diseases is to research and develop pure natural traditional Chinese medicines which have fewer side effects and can effectively treat coughs.
Asarum, as a traditional Chinese medicine, is firstly recorded in the Yellow Emperor's Internal Classic, and is classified as a top grade. 2010 edition of Chinese Pharmacopoeia stipulates that the source of Asarum is dried roots and rhizomes of Asarum Heterotropoides Fr. Schmidt var. Mandshuricum (Maxim.) Kitag., Asarum sieboldii Miq. var. seoulense Nakai, or Asarum sieboldii Miq. The Asarum is warm in nature, acrid in flavor, and attributive to heart, lung and kidney meridians, has the effects of relieving exterior syndrome and dispelling cold, dispelling wind and relieving pain, opening orifices, and warming the lung to dissipate phlegm retention, and is used for treating cough and asthma due to phlegm retention, wind-cold type common cold, headache, toothache, nasal congestion and discharge, allergic rhinitis, nasosinusitis, and Rheumatic arthralgia. Some ancient books record the use of Asarum for treating coughs, for example, the Yellow Emperor's Internal Classic records, “the Asarum has main indications for cough with dyspnea, headache during use of brains, . . . , and has the effects of freeing nine orifices”; Compendium of Materia Medica records, “acrid in flavor can clear lung, so it is suitable for use by patients with wind-cold type common cold and abnormal rising of qi”; Rihuazi Bencao records, “treating coughs, . . . , chest accumulation”; Changsha Yaojie records, “good at reducing adverse rising, designed to stop coughing”; and Medicinal Theory records, “treating cough with dyspnea, . . . ”. At present, reports for literature about the antitussive effect of Asarum mostly focus on compound methyleugenol of total volatile oil (Zhou Huiqiu, Study on Pharmacological Effects of Methyleugenol, Acta Chinese Medicine and Pharmacology, 2000, (2):79-80). Also, the study on non-volatile components of Asarum is rarely reported, and only the isolation of non-volatile constituents, including kakuol, 1-asarinin, 1-sesamin, aristololactam I, kaempferol-3-O-glucoside and the like, from the roots and rhizomes of Asarum is reported (Cai Shaoqing, Study on Non-Volatile Chemical Constituents of Asarum Heterotropoides Fr. Schmidt var. Mandshuricum (Maxim.) Kitag., Journal of Beijing Medical University, 1996, 28(3):228-230; Lv Shuai, Isolation and identification of chemical constituents from roots of Asarum Heterotropoides Fr. Schmidt var. Mandshuricum (Maxim.) Kitag. (II), Journal of Shenyang Pharmaceutical University, 2010, 27(9): 707-710; Wei Qingchun, Isolation and Identification of Chemical Constituents of Asarum sieboldii Miq. var. seoulense Nakai, Li Shizhen Medicine and Materia Medica Research, 2010, 21(3): 676-677). A preparation method of Asarum polysaccharide has been studied and reported (Li Jingjing, Study on the Separation, Purification and Immunological Activity of Polysaccharide from Asarum Heterotropoides, Journal of Changchun Normal University (Natural Science), 2008, 27(1): 54-58), but this preparation method needs to extract three times, the extracting cycle each time is longer (6 hours), and the centrifugation treatment is required in the preparation process, therefore, this method is not suitable for industrial mass production; with adoption of this preparation method, the overall yield of polysaccharides is lower (9.56 wt %), and the content of saccharides is also lower (48 wt % to 52 wt %); in addition, it is reported that Asarum polysaccharide, the non-volatile constituent of Asarum, has an effect of promoting the proliferation of mouse spleen lymphocytes T and B (Li Jingjing, Study on the Separation, Purification and Immunological Activity of Polysaccharide from Asarum Heterotropoides, Journal of Changchun Normal University (Natural Science Edition), 2008, 27(1): 54-58). However, the studies and reports about the antitussive activity of Asarum total polysaccharide, the non-volatile constituent of Asarum, have not been seen at present.